The long term objective of this proposal is to understand the pathologic mechanisms behind the disease amyotrophic lateral sclerosis (ALS). Recently, the protein TDP-43 was identified in inclusions in motor neurons of patients with sporadic ALS, and mutations in TDP-43 have been found to be responsible for a subset of familial cases of ALS. The proposed research seeks to identify the consequences of TDP-43 aggregation in neurons and identify mechanisms by which potentially toxic TDP-43 aggregates can be cleared from affected cells. A key aspect of this proposal is to develop a model of TDP-43 toxicity in Drosophila melanogaster. TDP-43 will be expressed in the neurons of flies, and phenotypes associated with TDP-43 toxicity will be analyzed. Genetic techniques, including unbiased screens, will then be used to identify factors that abrogate these phenotypes. Genes identified in these assays could lead to new understanding of disease mechanisms or become future targets of therapy. In addition, the role of Ubiquilin, a recently identified TDP-43-interacting protein, will be explored using this model. Ubiquilin is intimately involved in the unfolded protein response, and it is thought that this protein has a protective function in neurons. This hypothesis will be directly tested in vivo using Drosophila. Another goal of this proposal is to determine the role of autophagy in the degradation of TDP-43 inclusions. Autophagy is the bulk degradation of cytoplasmic components, including misfolded and aggregated proteins, and is critical for normal neuronal homeostasis. Pharmacologic, microscopic, and biochemical techniques will be used to explore the hypothesis that autophagy is involved in TDP-43 aggregate clearance. In addition, the Drosophila model described above will also be used to address this question in vivo.